It is known that in certain procedures of producing aromatic polyester-carbonates small amounts of certain molecular weight regulators or chain terminators can be used to provide end or terminal groups on the polyester-carbonate and thereby control the molecular weight of the polymer. Such materials include chroman, phenol and p-tertiary-butylphenol.
The prior art also discloses several other types of compounds that act as chain terminators for polycarbonates. Thus, U.S. Pat. No. 3,085,992 discloses alkanol amines as chain terminators; U.S. Pat. No. 3,399,172 teaches imides as chain terminators; U.S. Pat. No. 3,275,601 discloses that aniline and methyl aniline function as chain terminators in the interfacial polymerization process for producing polycarbonates; and U.S. Pat. No. 4,001,184 discloses primary and secondary amines as molecular weight regulators for polycarbonate. Furthermore, U.S. Pat. No. 3,028,365 discloses that aromatic amines and other monofunctional compounds can be used to control or regulate the molecular weight of the polycarbonate, thereby forming aryl carbamate terminal groups. Aromatic polycarbonates having carbamate end groups are disclosed in U.S. Pat. No. 4,111,910. These polycarbonates are prepared using a terminating amount of ammonia, ammonium compounds, primary cycloalkyl, aliphatic or aralkyl amines and secondary cycloalkyl, alkyl or aralkyl amines, and chroman-I.
However, according to Schnell, Chemistry and Physics of Polycarbonates (1964), page 183, ammonium hydroxide and amines saponify polycarbonates back to the monomers, i.e., bisphenol A. This is supported by Bolgiano in U.S. Pat. No. 3,223,678 wherein he indicates that small amounts of amines such as monoethanolamine and morpholine break or degrade the polycarbonates into lower molecular weight polycarbonates. Thus, this area of chain terminators for polycarbonates is generally not very well understood and is one where the empirical approach is still generally the rule in determining whether a particular compound or class of compounds will function as effective chain terminators in polycarbonates.
The same uncertainty which is present in the case of polycarbonate resins also holds true for polyester-carbonate resins. This area is further complicated by the fact that not only must a particular compound act as a chain terminator, but this compound when incorporated into the polyester-carbonate polymer as a terminal group must not adversely affect the physical properties of the polyester-carbonate. Thus, while some compounds may be effective chain terminators they are not practical since when they are incorporated into the polymer as terminal groups they adversely affect the physical properties of the polyester-carbonate.